Unilateral and Bilateral Isokinetic Leg Extensions Exhibit No Differences in Neuromuscular Excitation Under Maximal and Fatiguing Conditions

Anders, JPV, Neltner, TJ, Smith, RW, Arnett, JE, Housh, TJ, Schmidt, RJ, and Johnson, GO. Unilateral and bilateral isokinetic leg extensions exhibit no differences in neuromuscular activation under maximal and fatiguing conditions. J Strength Cond Res38(3): 474–480, 2024—The bilateral deficit is a phenomenon where force production during a bilateral (BL) muscle action is less than the sum of force produced when the muscle action is performed unilaterally (UL) with both limbs. The purpose of this study was to compare peak force, electromyographic (EMG) amplitude (AMP), and mean power frequency (MPF) of the nondominant leg between UL and BL isokinetic leg extensions. Eleven recreationally trained men (mean ± SD; age = 20.8 ± 1.7 years; body mass = 84.0 ± 16.2 kg; height = 179.3 ± 7.2 cm) volunteered to participate in this study. The 2 test visits included UL and BL maximal isokinetic leg extensions at 180°·second−1followed by a fatiguing task of either 50 UL or 25 UL followed immediately by 25 BL (ULBL) maximal, isokinetic leg extensions at 180°·second−1, in random order on separate days. The results demonstrated a significant (p= 0.015, ηp2= 0.460) bilateral deficit in force (UL = 56.29 ± 11.20 kg; BL = 50.32 ± 7.35 kg; d= 0.63; 95% CI [1.42, 10.52]) but no significant bilateral deficit in EMG AMP (p= 0.892, ηp2= 0.002). The peak force during the fatiguing task demonstrated a significant main effect for repetition (p< 0.001, ηp2= 0.943) characterized by a reduced peak force from repetitions 20–50. Similarly, EMG MPF demonstrated a significant main effect for repetition (p< 0.001, ηp2= 0.702) characterized by a reduced EMG MPF from repetitions 35–50. There were no significant effects (p= 0.102–0.387, ηp2= 0.096–0.203) for EMG AMP. These findings suggested that the bilateral deficit was not associated with a neuromuscular deficit and UL muscle actions may be used to potentiate force production of subsequent BL muscle actions.